I am the type of user that uses CGam in order to snap pictures, and then uses native Sailfish apps in order to share them (Telegram Fernschreiber, Facebook through browser, etc.).
The problem was that the SFOS Gallery app would not show pictures from the android_storage/DCIM, although there is a whitelist line in the Pictures.permission file.
I solved this by creating a symlink in the /home/defaultuser/Pictures folder:
ln -s /home/defaultuser/android_storage/DCIM /home/defaultuser/Pictures
This is for other ppl who face the same issue like me.
If there is any matter of security tampering when using this method, please let me know!